The four holes visible on the back of the Eufrodite symbolize the four hidden powerful bass drivers and this driver lineup is responsible for Eufrodite ’s very potent incredible precise and deep bass performance. The acoustical unique filter is the perfect tool to enhance seemliness integration of bass/midrange with wonderful timing and clarity.  It is very rewarding when you remove filter coils and capacitors from the bas drivers so the amplifier can work direct (filter components is slowing the membranes stop and start movements). The Eufrodite is also working without filter components and this is a perfect solution for a high-end full range working loudspeaker. Over the years I tried everything to get one drive unit to play as a full range loudspeaker but no one was able to do it. It always lacked true realism in bass performance and the midrange always lacked true body in its sound, the midrange had always more less a bright screaming character. The Eufrodite has it all, deep bas, tremendous clarity, fantastic timed dynamic musical sound.